1. Field of the Invention
This invention relates to a method for providing high density, strain relief interconnections between two circuitized substrates.
2. Prior Art
With the advent of large scale integration and other related technologies, it has become increasingly important to be able to provide high density, fine line interconnection capabilities for interconnects between two or more substrates. This requirement is even more difficult, if the two substrates are relatively large and have different coefficients of expansion, which would necessitate that some strain relief capability be built into the configuration.
An early technique for minimizing the mechanical stresses obtained during chip joining is shown in the article entitled "Semiconductor Chip Joining" in the IBM Technical Disclosure Bulletin, Volume 10, No. 5, October 1967 at pages 657 and 658. This article describes the use of soluble standoffs in connection with preformed interconnection leads mounted on a decal type support and using either a solder reflow technique or a pressure joining to interconnect the electrodes. Following the interconnection, the support decal is removed and the solvent soluble material is dissolved leaving a flexible, bent interconnection which transmits less stress to the interconnected joints. This technique is satisfactory for low density, relatively wide interconnections that can be easily aligned, but does not readily yield itself to a high density, fine line interconnection technique. Furthermore, it requires that the interconnecting members be preformed prior to being applied between the two substrates.
U.S. Pat. No. 3,428,866 teaches the use of removable powdered material as a bridging material over which interconnections can be formed. This technique does permit, for example, the growing by electroless deposition of interconnections between adjacent substrates, but does not yield strain relieved interconnections. Furthermore, the use of the powdered material as a bridging material, limits the minimum size that can be obtained because of the inherent graininess of the bridging material.
Still other difficulties are encountered in providing such interconnections, such as for example by beam lead technology, in situations where the interconnecting technologies inherently develop relatively high heat. Certain technology processes, such as bubble memory and Josephson packages, preclude the use of temperatures approaching or exceeding 150.degree. C. Individual bonding of preformed wires to make the interconnections in such applications is very costly and difficult to accomplish with a high degree of reliability.